Silyl Pincer Transition Metal Complexes for Challenging Bond Activation and Catalysis

Transition metal catalysts play a key role in facilitating chemical processes that convert abundant raw material resources into value-added products (pharmaceuticals, flavors, fragrances, plastics, etc.) in an efficient, selective manner. Chemists have long focused on developing homogeneous catalysts that utilize scarce precious metals such as Pd, Pt, Rh, and Ru. Despite their efficacy, such catalysts are limited by the decreasing availability, and associated high cost, of the late 4d- and 5d-transition metals. Mining and processing of ores containing such metals is also highly energy intensive, generating large CO2 emissions. Faced with the pressing need to develop increasingly sustainable synthetic processes, interest in the reactivity of earth-abundant 3d-metals, such as Mn, Fe, Co, and Ni has grown significantly, with the goal of discovering new, effective catalysts to complement, and possibly supplant, precious metal-based technology. While nature has utilized 3d-transition metals almost exclusively for catalyzing chemical reactivity, harnessing this reactivity has proven challenging in the laboratory. In this regard, this proposal targets the development of new classes of broadly useful, sustainable 3d-metal catalysts for atom economical alkene and alkyne hydrofunctionalization, a class of widely used reactions for converting such feedstocks into consumer products. Our strategy builds upon our established success in developing highly reactive precious metal silyl pincer complexes. We seek to extend this ligation strategy to the 3d-metals, where we anticipate that silyl-metal cooperativity in element-hydrogen bond cleavage may provide reactivity advantages in hydrofunctionalization catalysis. While earth-abundant 3d-metal catalysts are highly desirable and will be our primary focus, the utility of precious metal complexes for targeted, challenging reactivity applications cannot yet be discounted. As such, a second area of investigation will target the development of new catalytic amination reactions facilitated by Ir silyl pincer species. Due to the prevalence of N-containing functional groups in pharmaceuticals and fine chemicals, significant interest exists in developing new atom-economical amination reactions, especially reactions that utilize ammonia - an inexpensive commodity chemical. Our group has established that Ir silyl pincer complexes can undergo challenging stoichiometric N-H bond oxidative addition reactions to cleave the N-H bonds of amines, including ammonia. In this proposal, we seek to capitalize on this novel reactivity in order to develop new catalytic processes for the functionalization of amines and ammonia, which would have wide applicability in chemical synthesis. The proposed studies will advance our understanding of transition metal mediated synthesis, will provide practical 3d-metal catalysts for uptake by end-users, and will provide world-class training for researchers in modern synthetic chemistry techniques.